I. Field of the Invention
The present invention relates generally to the fields of cell biology, developmental biology, cardiology and neurobiology. More particularly, it concerns methods and compositions relating to the differentiation of stem cells into cardiogenic or neurogenic cell types.
II. Description of Related Art
A. Cardiogenesis
Stem cell therapy and regenerative medicine are promising new frontiers in the treatment of myocardial infarction (MI) and heart failure. Yet, endogenous stem cell repair mechanisms are underpowered for repair of the tissue destruction associated with ischemic and non-ischemic cardiomyopathies. Thus, there is intense interest in developing therapeutic strategies or drugs to enhance the endogenous regenerative potential of the adult human myocardium. Alternatively, cardiogenic stem cell populations can be supplied to the heart exogenously, when and where needed to repair myocardial injury. Pre-delivery enhancement of stem/progenitor cell function by promoting cell growth, differentiation, survival, homing, or a combination of these, using small-molecule drugs or growth factors is an exciting new strategy that has been successful in clinical trials of peripheral vascular disease (Seeger et al., 2005; 2007; Sasaki et al., 2006; Dimmeler et al., 2001; Yamaguchi et al., 2003; Wojakowski et al., 2007). Cytokine mobilized PBMCs are a universally accessible source of autologous human stem/progenitor cells (Wojakowski et al., 2007). Despite the uncertainty regarding the cardiogenic plasticity of bone marrow-derived cells, clinical trials have moved forward at a rapid pace. Initial results from over a dozen worldwide trials using bone marrow-derived cells in MI and heart failure have demonstrated feasibility, safety and modest but definite clinical benefits, generating considerable optimism for the future of this therapy (Rosenzweig, 2006; Assmus et al., 2006; 2007; Schachinger et al., 2006a). Still, many basic scientific questions remain unanswered. To fulfill the clinical promise of stem/progenitor cells in cardiovascular repair, it is essential to clarify the roles of cardiomyogenesis, neovascularization, cell fusion (Nygren et al., 2004) and paracrine growth factor secretion (Dell'Era et al., 2003), since all of these mechanisms could contribute to the recovery of cardiac function (Dimmeler et al., 2005).
An enhanced understanding of cell fate mechanisms will also translate into greater clinical success of cardiovascular cell therapy (Assmus et al., 2006; Schachinger et al., 2006a; 2006b; Nadal-Ginard & Fuster, 2007). Recent studies indicate that cardiac muscle, vascular smooth muscle and endothelial cells share a common multi-potent progenitor heritage, the cardiovascular master stem cell, which has been identified in human myocardium (Wu et al., 2006; Moretti et al., 2006; Garry & Olson, 2006). However, despite decades of intensive investigation using traditional molecular, cellular and genetic experimental approaches, in vertebrate, invertebrate and stem cell models (Garry & Olson, 2006), much remains to be learned about the circuitry that drives cardiovascular fate specification.
Chemical genetics offers a new investigative approach to cardiovascular fate in stem cells (Ding & Schultz, 2004; Chen et al., 2006). High throughput technology allows libraries of hundreds of thousands of synthetic organic chemicals to be rapidly screened, identifying small-molecules that perform specific functions, through highly targeted interactions with proteins. Small-molecules can provide new probes to explore complex signaling networks and pathways. Importantly, bioactive small-molecules identified in chemical screens provide both highly versatile experimental probes to interrogate mechanistic hypotheses and serve as platforms for new drugs.
B. Neurogenesis/Brain Cancer
Unlike the heart, the brain has several repositories of stem/progenitor cells available to participate in repair and regeneration, yet much needs to be learned regarding the ability of these cells to proliferate, differentiate and migrate in response to physiologic and pathophysiologic stimuli within the central nervous system. Hippocampal neurogenesis, a mechanism for maintaining cellular homeostasis in the adult brain, plays an important functional role in higher cerebral activities like learning and memory. While exercise and exposure to an enriched environment promote adult hippocampal neurogenesis, chronic stress, depression, sleep deprivation and aging can decrease neural stem/progenitor cell proliferation in the adult hippocampus. Chemistry has an established role in governing neurogenesis; the stress-related glucocorticoid hormones inhibit, whereas anti-depressant medications enhance hippocampal neurogenesis. The ability to grow and maintain neural stem/progenitor cells in vitro in an undifferentiated, highly proliferative state provide a unique experimental system and opportunity to study chemical triggers of cell fate. Importantly, chemicals can be identified that not only strongly favor neuronal differentiation, but also actively suppress astrocyte and oligodendrocyte differentiation, two alternative fate choices available to these stem cells. Explorations of the chemical biology of adult neurogenesis have important implications for understanding the mechanisms of cell fate and provide new drug candidates to treat neurological conditions that involve neurogenesis.
As a corollary to the ability of a chemical compound to induce neurogenesis in a neural stem/progenitor cell, this sort of compound might also be an effective differentiation-inducing anti-neoplastic agent. Increasing evidence indicates that stem cells lie at the root of brain tumors like glioblastoma multiforme. Small-molecules that are active in neural stem/progenitor cells might therefore also have bioactivity against the brain tumor stem cell. Thus, small-molecules that induce neural stem cell differentiation might also be useful for arresting growth, killing or differentiating glioblastoma multiforme (GBM) cancer stem cells, currently thought to be the cause of one of the most devastating and incurable of human malignancies.